Osteosynthesis is achieved by immobilizing separate bone segments and in particular vertebral segments on either side of a failed or damaged disc. When trying to achieve osteosynthesis and specifically fusion between different segments of the spine, one has to provide some type of immobilization. There are various prior art systems and methods which try to achieve this purpose. The different systems involve the placement of implants which typically include pedicle screws threaded into the bone. The implants are then secured to each other by stabilizing or fixation rods.
Traditionally an open large incision is made exceeding the area to receive the implants. Such a large incision involves extensive stripping and/or cutting of musculature from the posterior elements. An implant system successfully used in the traditional approach is described in U.S. Publication No. 2007/0073291 (“291 publication”) which is assigned to the assignee of this application, SeaSpine, Inc. (“SeaSpine”). The contents of the '291 publication are incorporated herein by reference.
Recently the trend has been moving to less invasive techniques and the use of devices accommodating such techniques. A minimally invasive approach attempts to avoid a majority of this muscle stripping and subsequent morbidity by using dilators, to hold open a smaller incision, through which the implants can be inserted. Also, the minimally invasive technique usually relies on the dilators stretching the muscles out of the surgical path rather than cutting them, and the dilators can be placed between natural muscle planes to further avoid muscle damage. As is pointed out in An Anatomic Approach to Minimally Invasive Spine Surgery, by Perez-Cruet M J, Khoo L T, Fessler R G, Quality Medical Publishing, Inc. 2006, pg. 150-151:
“Many of the procedures have steep learning curves and require additional training to master, including fellowship training, cadaveric workshops, and animal laboratory study. However, once mastered, these techniques can result in a significant reduction of complications and postoperative pain and discomfort, and allow patients to return to their activities of daily living sooner than standard open, more conventional procedures.”
Various prior art minimally invasive techniques and devices for use therewith are discussed in the following U.S. patents and U.S. application publications:
US2005/0131421 (“'421 publication”); US2005/0085813 (“'813 publication”); US2005/0154389 (“'389 publication”); U.S. Pat. No. 6,530,929 (“'929 patent”); US 2006/0122597 (“'597 publication”); U.S. Pat. No. 7,160,300 (“'300 patent”); US2005/0131408 (“'408 publication”); US2006/0241600 (“'600 publication”); and US2006/007445 (“'445 publication”).
The above patents/publications disclose different types of implant systems and methods, including the use of a variety of access tubes, to enable a surgeon to install the implants in a relatively less invasive manner. In addition to the installation of the spinal implants, a fixation element, such as a rod, must be securely connected between the installed implants to insure that the distance and orientation of the implants relative to each other remains fixed.
It is the delivery of the spinal fixation rod to the installed implants in a reliable and minimally invasive manner which presents a major challenge. For example, the '421 publication teaches the use of angled guide member positioned at the distal end of one of the access sleeves to transition a loose fixation rod from its lengthwise orientation as it travels down one of the access tubes to a transverse orientation necessary for entering the transverse rod receiving opening in the adjacent implant. Among other shortcomings, it would appear that only a small portion of the rod could be seated in the rod receiving opening in the implant located beneath the guide through which the rod is inserted.
The '455 publication discloses the use of several different tools for positioning a fixation rod into the rod receiving openings in the installed implants. The insertion tools are either designed to penetrate the tissue surrounding the implants to deliver a separate fixed length rod or one positioned outside of the patient's body to deliver an elongated rod through the tissue to the implants with any excess rod being cut off in the surgical area.
The '589 publication, like the '455 publication, discloses the use of an angled guide member positioned at the distal end of an access sleeve to reorient a fixation rod in a transverse direction as it leaves the access sleeve and a rather complicated instrument for seating the reoriented rod in the implants. Such an instrument would not appear to be particularly compatible with a minimally invasive procedure.
The '813 publication discloses the insertion of a fixation rod pivotally mounted on the top of an implant through an access tube. The rotation of the rod serving to screw the pedicle screw of the implant into the underlying bone. The rod is then pivoted out through a slot in the tube and into the rod receiving opening in an adjacent implant with wires extending through the access tube and connected to the proximal end of the rod. The wires are controlled by a manually operated tool arrangement.
The '600 publication discloses a percutaneous pedicle screw assembly in which each pedicle screw is inserted through an access tube and then threaded into the underlying pedicle. Then a housing with a fixation rod pivotally mounted thereto, is assembled over the head of the screw on site via a split ring where the housing is open at the bottom or through a side opening in the housing. The assembly of the housing over the head of an installed pedicle screw deep inside a patient's body would be challenging to a surgeon to say the least. In addition, the method of deployment of the fixation rod from an orientation aligned with the access tube axis to a perpendicular alignment with minimal disturbance to the surrounding tissue is not disclosed.
The '408 publication discloses inner and outer coaxial access tubes designed to install fixed (versus polyaxial) bone anchors with the outer tube arranged to releasably engage the anchor. The placement of a fixation rod within the anchor is not addressed.
The '300 publication discloses several tools for installing a fixation rod into the rod accommodating opening in installed implants. The tools include a tubular guide extending from each implant to a location outside of the particular body with each guide having internal threads at the proximal end thereof to guide a set screw into the upper threaded portion of the implant. Each guide has a longitudinally extending slot therein for receiving the rod. A tool is disclosed for advancing the rod along each tubular guide. This arrangement would not appear to be particularly conducive to a minimally invasive procedure.
The '597 publication discloses the use of longitudinally slotted tubular extenders in which the distal ends thereof are arranged to mate with the collar of an implant. Several forms of adjuster tools are disclosed for adjusting the distance between implanted vertebrae. While installed fixation rods are disclosed the manner of inserting the rods to their final resting place within the implants is not addressed.
The '929 publication discloses a complicated tool for inserting a curved fixation rod within two or more installed implants. The tool does not appear to be particularly conducive to minimizing the disturbance of tissue around the surgical site.
It is believed that the steep learning curve required for mastering a minimally invasive approach discussed earlier is, in large part, due to the difficulties in inserting and securing the implants and fixation rods through the smaller incisions. Visualization is limited and most of the manipulation of the implants and fixation rods must occur deep within the incision. This invention addresses these difficulties by creating an improved method for the surgeon to insert the implants and deploy a fixation rod in a minimally invasive fashion, through the use of specially designed approach instrumentation and implants.